Electromechanical switches with dimensions in the micrometer and nanometer range, also referred to as micro-electromechanical (MEM) and nano-electromechanical (NEM) switches, are considered to be an attractive alternative to traditional solid state switches, such as, e.g., transistors and pin diodes. This is due to a more ideal switching characteristic (low-loss, linearity, steep switching) while having a smaller power requirement. In contrast to a solid state switch, a switching operation carried out by means of an electromechanical switch includes the mechanical actuation or movement of two switch portions relative to each other between a disconnected (“open”) position and a connected (“closed”) position, thereby preventing or allowing the flow of electricity through an electrical circuit.
MEM switches are for example targeting RF (radio frequency) applications such as e.g. in phased arrays and reconfigurable apertures for telecommunication systems, switching networks for satellite communications, and single-pole N-throw switches for wireless applications (portable units and base stations). More recently, NEM switches have been developed driven by the promise of a more ideal and lower power switching element for logic applications. Such switches may provide attributes like a near zero leakage, a very steep subthreshold slope with a mechanical delay of the order of nanoseconds and an electrical time constant of the order of picoseconds.
The attractiveness of electromechanical switching technology may, however, be limited by a relatively poor reliability. In particular, reliable electrical switching for a very large number of switching cycles may turn out to be difficult. Electromechanical switching has indeed been commercialized for applications for which the number of switching events is moderate (<107), e.g. RF application in radar systems, wireless communication and instrumentation. However, a large spectrum of applications would require switching cycles of higher orders of magnitude. As an example, logic applications may require 1012 (e.g. remote electronic, automotive, space applications) to 1016 (processor) cycles.
As a consequence, significant research is focusing on this subject, mainly by optimization of materials used for electrical contacts of the switch devices (e.g. usage of noble metals and conductive oxides) or by developing high force actuators (e.g. application of piezoelectric actuation in contrast to simpler electrostatic actuation). Even though such concepts have led to some improvement on the switching reliability, it is still far from the requirements concerning e.g. logic applications and demanding RF applications. In addition, such approaches may require more complex micromechanical structures and less standard materials, which has an impact on the fabrication cost of such devices.
U.S. Pat. No. 7,486,163 B2 describes an electromechanical switch structure including a fixed electrode and a movable electrode. The movable electrode is actuated by applying a voltage potential between the two electrodes. In order to effect the switching operation with a lower voltage, a modulation of the voltage potential is proposed. This is done in such a way as to inject energy into the mechanical system until there is sufficient energy in the system to achieve the actuation. At this, it is intended to bring the mechanical system into a resonant state. For this purpose, a feedback control system is applied in order to adapt the frequency of the modulation to the resonant frequency of the mechanical system, because the resonant frequency changes in the course of the actuation of the switch structure.
The aforesaid concept relates to the application of a lower voltage potential for actuation of the switch, and not to providing an improved switching reliability. Furthermore, the switch has a relatively complex design due to the provision of the feedback control system.